# -*- coding: utf-8 -*- 
# @project : 《Atcoder》
# @Author : created by bensonrachel on 2021/7/21
# @File : （step2）E - Equation（CF）.py
# https://codeforces.com/edu/course/2/lesson/6/2/practice/contest/283932/problem/E

import sys

#又是一道非整数的二分

def bi_Equation(c):
    l = 0
    r = c
    for _ in range(100):  # Usually, you can always write 100 iterations and not think.
        mid = (l + r) / 2  # float类型
        if (mid * mid + mid ** 0.5 <= c):
            l = mid
        else:
            r = mid
    return r


if __name__ == "__main__":
    c = float(sys.stdin.buffer.readline())
    res = bi_Equation(c)
    print(res)

"""
**这种求幂的方法只适合正数。

返回l r都ac
"""